During the production of propylene oxide, the product stream undergoes a caustic wash treatment to remove methyl formate prior to product purification. The propylene oxide product stream that is treated by the caustic wash contains propylene oxide and a large quantity of aldehydes (roughly about 2.5 wt %, primarily acetaldehyde).
Under highly alkaline conditions, lower molecular weight aldehydes, such as acetaldehyde (ethanal), readily undergo base catalyzed aldol condensation at ambient or higher temperatures. The result of such aldol condensation and related reactions is the formation of oligomers and polymers which precipitate out of the wash solution as viscous oils, polymeric gums, and solids. These precipitates can foul the processing equipment and result in the reduction of processing throughput and costly equipment maintenance or repair.
Effective and economical methods are needed for retarding aldol condensation and related reactions during caustic washing of a propylene oxide product stream in order to increase unit run length, reduce maintenance costs, reduce hazardous waste disposal costs, increase production, and reduce personnel exposure.